Retrieval and Evaluation of Ice Water Content from the Airborne Wyoming Cloud Radar in Orographic Wintertime Clouds during SNOWNIE
Abstract The ice water content (IWC) in ice and mixed-phase clouds is retrieved from airborne Wyoming Cloud Radar (WCR) measurements aboard the University of Wyoming King Air (UWKA), which has a suite of integrated in situ IWC, optical array probes (OAP) and remote sensing measurements and provides a unique dataset for this algorithm development and evaluation. A sensitivity study with different idealized ice particle habits shows that the retrieved IWC with aggregate ice particle habit agrees the best with the in situ measurement, especially in ice or ice-dominated mixed-phase clouds with a correlation coefficient (rr) of 0.91 and close-to-zero bias. For mixed-phase clouds with ice fraction ratio less than 0.8, the variances of IWC estimates increase (rr = 0.76) and the retrieved mean IWC is larger than in situ IWC by a factor of 2. This is found to be related to the uncertainty of in situ measurements, the large cloud inhomogeneity, and the retrieval assumption uncertainty. The simulated reflectivity (Ze) and IWC relationships assuming three idealized ice particle habits and measured particle size distributions show that hexagonal columns with the same Ze have a lower IWC than aggregates, whose Ze-IWC relation is more consistent with the observed WCR Ze and in-situ IWC relation in those clouds. The 2DS images also indicate that ice particle habit transition occurs in orographic mixed-phase clouds, hence the retrieved IWC assuming modified Gamma PSD of aggregate particles tends to be biased larger in this kind of clouds.